Oil Pressure Switch

[russell]

Hi,

Read a post on how to check the oil pressure sensor as the oil light does not come on. Unplugged the wires, turned key on, grounded each wire, nothing. Removed the sensor and sprayed carb cleaner in the sensor. Question? how easy should the plunger move, i'm finding i have to stick a screw driver in and tap it to move the plunger. I'm thinking the plunger should move freely!!!

Connected it all up and still the oil light does not come on. Where to from here????

[natemoen]

Did you check to see if the light bulb is burnt out?

[TopCatGr58]

Yes, the switch does have a weak spring in it so you will feel a little resistance. Like Nate said you want to make sure the bulb works. It should light up when you turn the key on before starting, and then go out once running. If not on with just key on, then bulb probably burnt out.

[motoman]

Might also, if bulb works, remove the pressure switch and blow it clean with Brake-Kleen and re-install.

[russell]

Checked the connection with a circuit tester. Has power from the light panel. Changed the bulb over from one that was working. Checked the circuit all the way down to the oil pressure switch switch, power all the way through, yet the light still doesn't come on. What am I missing here?

[mack]

Light

The light won't come on in a running motor if it's working correctly. I remember Crazy steve explaining this several months ago. When no pressure is there, contact is maintained and the light stay's on. When the oil is flowing through the system, it forces the switch open, breaking contact and the light goes off. Thats why at start up the light only flickers on for a second, then goes out.

[crazy steve]

All the pressure sensor does is supply the ground for the indicator light; if grounding the wire to the sensor doesn't light a known good bulb, the problem is in the wiring, not the sensor. If you do have 12V power coming to the sensor and a good lamp doesn't light when grounding the wire, then the problem is either a misconnection somewhere or a shorted out lamp socket. At the socket, power should come into it on the center pin for the lamp and go out to the sensor on the socket outer shell. With a lamp installed, you should read about 20 ohms between the input wire and the outer shell (the resistance of the lamp when cold).

Now after correcting that, you may still have a bad pressure switch. If it's been sending 12V to the switch and the light isn't coming on, that's basically a dead short and it may have damaged the contacts in the switch. To check that, check for continuity between the sensor body and it's wire connection. At rest (with the motor not running), you should have continuity between these. With the motor running, this should go 'open' (no continuity). Make sure you have continuity between the sensor body and the battery ground also; if the sensor has been installed with any sort of thread sealer, that can interfere with the electrical connection between the sensor and the engine cases.